Add a bit about adding, moving and copying files for patches.

Differential Revision:	https://reviews.freebsd.org/D1052
Reviewed by:	wblock
Sponsored by:	Absolight
Enhance the Poudriere chapter a great bit.

Differential Revision:	https://reviews.freebsd.org/D770
Submitted by:	riggs
Reviewed by:	wblock
Sponsored by:	Absolight